On Mon, Feb 15, 2021 at 4:38 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Saravana, > > On Fri, Feb 12, 2021 at 4:00 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > On Thu, Feb 11, 2021 at 5:00 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > > - I2C on R-Car Gen3 does not seem to use DMA, according to > > > /sys/kernel/debug/dmaengine/summary: > > > > > > -dma4chan0 | e66d8000.i2c:tx > > > -dma4chan1 | e66d8000.i2c:rx > > > -dma5chan0 | e6510000.i2c:tx > > > > I think I need more context on the problem before I can try to fix it. > > I'm also very unfamiliar with that file. With fw_devlink=permissive, > > I2C was using DMA? If so, the next step is to see if the I2C relative > > probe order with DMA is getting changed and if so, why. > > More detailed log: > > platform e66d8000.i2c: Linked as a consumer to e6150000.clock-controller > platform e66d8000.i2c: Linked as a sync state only consumer to e6055400.gpio > > Why is e66d8000.i2c not linked as a consumer to e6700000.dma-controller? Because fw_devlink.strict=1 is not set and dma/iommu is considered an "optional"/"driver decides" dependency. > platform e6700000.dma-controller: Linked as a consumer to > e6150000.clock-controller Is this the only supplier of dma-controller? > platform e66d8000.i2c: Added to deferred list > platform e6700000.dma-controller: Added to deferred list > > bus: 'platform': driver_probe_device: matched device > e6700000.dma-controller with driver rcar-dmac > bus: 'platform': really_probe: probing driver rcar-dmac with > device e6700000.dma-controller > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > > bus: 'platform': driver_probe_device: matched device e66d8000.i2c > with driver i2c-rcar > bus: 'platform': really_probe: probing driver i2c-rcar with device > e66d8000.i2c > > I2C becomes available... > > i2c-rcar e66d8000.i2c: request_channel failed for tx (-517) > [...] > > but DMA is not available yet, so the driver falls back to PIO. > > driver: 'i2c-rcar': driver_bound: bound to device 'e66d8000.i2c' > bus: 'platform': really_probe: bound device e66d8000.i2c to driver i2c-rcar > > platform e6700000.dma-controller: Retrying from deferred list > bus: 'platform': driver_probe_device: matched device > e6700000.dma-controller with driver rcar-dmac > bus: 'platform': really_probe: probing driver rcar-dmac with > device e6700000.dma-controller > platform e6700000.dma-controller: Driver rcar-dmac requests probe deferral > platform e6700000.dma-controller: Added to deferred list > platform e6700000.dma-controller: Retrying from deferred list > bus: 'platform': driver_probe_device: matched device > e6700000.dma-controller with driver rcar-dmac > bus: 'platform': really_probe: probing driver rcar-dmac with > device e6700000.dma-controller > driver: 'rcar-dmac': driver_bound: bound to device 'e6700000.dma-controller' > bus: 'platform': really_probe: bound device > e6700000.dma-controller to driver rcar-dmac > > DMA becomes available. > > Here userspace is entered. /sys/kernel/debug/dmaengine/summary shows > that the I2C controllers do not have DMA channels allocated, as the > kernel has performed no more I2C transfers after DMA became available. > > Using i2cdetect shows that DMA is used, which is good: > > i2c-rcar e66d8000.i2c: got DMA channel for rx > > With permissive devlinks, the clock controller consumers are not added > to the deferred probing list, and probe order is slightly different. > The I2C controllers are still probed before the DMA controllers. > But DMA becomes available a bit earlier, before the probing of the last > I2C slave driver. This seems like a race? I'm guessing it's two different threads probing those two devices? And it just happens to work for "permissive" assuming the boot timing doesn't change? > Hence /sys/kernel/debug/dmaengine/summary shows that > some I2C transfers did use DMA. > > So the real issue is that e66d8000.i2c not linked as a consumer to > e6700000.dma-controller. That's because fw_devlink.strict=1 isn't set. If you need DMA to be treated as a mandatory supplier, you'll need to set the flag. Is fw_devlink=on really breaking anything here? It just seems like "permissive" got lucky with the timing and it could break at any point in the future. Thought? -Saravana
